I think it comes from the conservative mindset that someone competent and capable in one field will be similarly competent and capable in other fields

Simply put: They believe in a hierarchy. Some people are imherently better at everything than others

She was competent and capable in her previous role of being an ass kisser. Because she was able to butter Trump up, it was assumed she would be good at any role, and she had “the look” Trump wanted (she looked like his daughter)